Vettel dazzled under the lights of the Marina Bay Street Circuit in the second practice session on Friday, again crushing his rivals as Red Bull team-mate Mark Webber was the only driver to finish within a second of the three-times world champion.
After back-to-back wins in Belgium and Italy these past few weeks to strengthen his grip on his current title lead, a third consecutive victory is on the cards.
Vettel, however, has no doubt Mercedes pair Hamilton and Rosberg - with eight poles between them in the last 10 races - will be hot on his tail.
After finishing six tenths of a second ahead of Webber with a lap of one minute 44.249secs, Vettel said: "I got a good lap to be honest.
"The time we set was a surprise, but I don't think it's completely representative, even though we are quick.
"But I think Mercedes will be very, very competitive once we go into qualifying."
Hamilton had dominated first practice, but in the second session the team focused on long-run pace, while a potential flying lap on the considerably faster supersoft tyre was ruined by traffic.
That left the 28-year-old, in desperate need of a win to close the 81-point gap to Vettel, 1.1secs down in fourth, with Rosberg just ahead of him.
"It wasn't the perfect Friday, but we got on with our programme and know where we have to make improvements," assessed Hamilton.
"The balance of the car felt really good in P1, but in P2 it felt terrible, which - surprise, surprise - is how it always is on a Friday, so there is a lot of work to do, but we're used to that.
"As it's so difficult to overtake at this circuit you naturally want to qualify as high up as possible.
"Of course the aim is for the front row, but that will be tough. It's not looking good at the moment.
"We'll give it everything we've got, but we don't have a second in the tank, that's for sure."
As for fellow title long-shots in Ferrari's Fernando Alonso and Kimi Raikkonen in his Lotus - 53 and 88 points down on Vettel respectively - they were sixth and eighth on the timesheet.
Alonso was almost 1.5secs back, with Jenson Button in his McLaren and Raikkonen in close attendance.
Raikkonen's team-mate in Romain Grosjean outshone the Finn as he was fifth fastest, 1.162secs down.
Alonso said: "We can't say this was a good start because we weren't competitive.
"But if we consider that last year, at the end of a difficult weekend we managed to get on the podium, we definitely aren't throwing in the towel yet."